all: add emulation support for Cortex-M3 with QEMU

Makefile

@@ -62,7 +62,7 @@ clean:
 	@rm -rf build
 
 fmt:
-	@go fmt . ./compiler ./ir ./src/examples/* ./src/machine ./src/runtime ./src/sync
+	@go fmt . ./compiler ./ir ./src/device/arm ./src/examples/* ./src/machine ./src/runtime ./src/sync
 	@go fmt ./testdata/*.go
 
 test:

main.go

@@ -330,6 +330,32 @@ func Run(pkgName string) error {
 	return nil
 }
 
+// Compile and run the given program in an emulator.
+func Emulate(pkgName, target string) error {
+	spec, err := LoadTarget(target)
+	if err != nil {
+		return err
+	}
+	if len(spec.Emulator) == 0 {
+		return errors.New("no emulator configured for this target")
+	}
+
+	return Compile(pkgName, ".elf", spec, false, false, false, "", func(tmppath string) error {
+		args := append(spec.Emulator[1:], tmppath)
+		cmd := exec.Command(spec.Emulator[0], args...)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		err := cmd.Run()
+		if err != nil {
+			if err, ok := err.(*exec.ExitError); ok && err.Exited() {
+				// Workaround for QEMU which always exits with an error.
+				return nil
+			}
+		}
+		return err
+	})
+}
+
 func usage() {
 	fmt.Fprintf(os.Stderr, "usage: %s command [-printir] [-target=<target>] -o <output> <input>\n", os.Args[0])
 	fmt.Fprintln(os.Stderr, "\ncommands:")
@@ -395,31 +421,32 @@ func main() {
 			fmt.Fprintln(os.Stderr, "error:", err)
 			os.Exit(1)
 		}
-	case "clean":
-		// remove cache directory
-		dir := cacheDir()
-		err := os.RemoveAll(dir)
-		if err != nil {
-			fmt.Fprintln(os.Stderr, "cannot clean cache:", err)
-			os.Exit(1)
-		}
-	case "help":
-		usage()
 	case "run":
 		if flag.NArg() != 1 {
 			fmt.Fprintln(os.Stderr, "No package specified.")
 			usage()
 			os.Exit(1)
 		}
-		if *target != llvm.DefaultTargetTriple() {
-			fmt.Fprintf(os.Stderr, "Cannot run %s: target triple does not match host triple.", *target)
-			os.Exit(1)
+		var err error
+		if *target == llvm.DefaultTargetTriple() {
+			err = Run(flag.Arg(0))
+		} else {
+			err = Emulate(flag.Arg(0), *target)
 		}
-		err := Run(flag.Arg(0))
 		if err != nil {
 			fmt.Fprintln(os.Stderr, "error:", err)
 			os.Exit(1)
 		}
+	case "clean":
+		// remove cache directory
+		dir := cacheDir()
+		err := os.RemoveAll(dir)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "cannot clean cache:", err)
+			os.Exit(1)
+		}
+	case "help":
+		usage()
 	default:
 		fmt.Fprintln(os.Stderr, "Unknown command:", command)
 		usage()

src/device/arm/semihosting.go

@@ -0,0 +1,63 @@
+package arm
+
+// Semihosting commands.
+// http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjhiea.html
+const (
+	// Regular semihosting calls
+	SemihostingClock      = 0x10
+	SemihostingClose      = 0x02
+	SemihostingElapsed    = 0x30
+	SemihostingErrno      = 0x13
+	SemihostingFileLen    = 0x0C
+	SemihostingGetCmdline = 0x15
+	SemihostingHeapInfo   = 0x16
+	SemihostingIsError    = 0x08
+	SemihostingIsTTY      = 0x09
+	SemihostingOpen       = 0x01
+	SemihostingRead       = 0x06
+	SemihostingReadByte   = 0x07
+	SemihostingRemove     = 0x0E
+	SemihostingRename     = 0x0F
+	SemihostingSeek       = 0x0A
+	SemihostingSystem     = 0x12
+	SemihostingTickFreq   = 0x31
+	SemihostingTime       = 0x11
+	SemihostingTmpName    = 0x0D
+	SemihostingWrite      = 0x05
+	SemihostingWrite0     = 0x04
+	SemihostingWriteByte  = 0x03
+
+	// Angel semihosting calls
+	SemihostingEnterSVC        = 0x17
+	SemihostingReportException = 0x18
+)
+
+// Special codes for the Angel Semihosting interface.
+const (
+	// Hardware vector reason codes
+	SemihostingBranchThroughZero = 20000
+	SemihostingUndefinedInstr    = 20001
+	SemihostingSoftwareInterrupt = 20002
+	SemihostingPrefetchAbort     = 20003
+	SemihostingDataAbort         = 20004
+	SemihostingAddressException  = 20005
+	SemihostingIRQ               = 20006
+	SemihostingFIQ               = 20007
+
+	// Software reason codes
+	SemihostingBreakPoint          = 20020
+	SemihostingWatchPoint          = 20021
+	SemihostingStepComplete        = 20022
+	SemihostingRunTimeErrorUnknown = 20023
+	SemihostingInternalError       = 20024
+	SemihostingUserInterruption    = 20025
+	SemihostingApplicationExit     = 20026
+	SemihostingStackOverflow       = 20027
+	SemihostingDivisionByZero      = 20028
+	SemihostingOSSpecific          = 20029
+)
+
+// Call a semihosting function.
+// TODO: implement it here using inline assembly.
+//go:linkname SemihostingCall SemihostingCall
+func SemihostingCall(num int, arg uintptr) int

src/runtime/runtime_qemu.go

@@ -0,0 +1,45 @@
+// +build qemu
+
+package runtime
+
+// This file implements the Stellaris LM3S6965 Cortex-M3 chip as implemented by
+// QEMU.
+
+import (
+	"device/arm"
+	"unsafe"
+)
+
+type timeUnit int64
+
+const tickMicros = 1
+
+var timestamp timeUnit
+
+//go:export Reset_Handler
+func main() {
+	preinit()
+	initAll()
+	mainWrapper()
+	arm.SemihostingCall(arm.SemihostingReportException, arm.SemihostingApplicationExit)
+	abort()
+}
+
+func sleepTicks(d timeUnit) {
+	// TODO: actually sleep here for the given time.
+	timestamp += d
+}
+
+func ticks() timeUnit {
+	return timestamp
+}
+
+//go:volatile
+type regValue uint32
+
+// UART0 output register.
+var stdoutWrite *regValue = (*regValue)(unsafe.Pointer(uintptr(0x4000c000)))
+
+func putchar(c byte) {
+	*stdoutWrite = regValue(c)
+}

target.go

@@ -21,6 +21,7 @@ type TargetSpec struct {
 	CompilerRT  bool     `json:"compiler-rt"`
 	PreLinkArgs []string `json:"pre-link-args"`
 	Objcopy     string   `json:"objcopy"`
+	Emulator    []string `json:"emulator"`
 	Flasher     string   `json:"flash"`
 	OCDDaemon   []string `json:"ocd-daemon"`
 	GDB         string   `json:"gdb"`

targets/cortex-m.s

@@ -0,0 +1,61 @@
+// Generic Cortex-M interrupt vector.
+// This vector is used by the QEMU target.
+
+.syntax unified
+
+// This is a convenience function for QEMU semihosting support.
+// At some point, this should be replaced by inline assembly.
+.section .text.SemihostingCall
+.global  SemihostingCall
+.type    SemihostingCall, %function
+SemihostingCall:
+    bkpt 0xab
+    bx   lr
+
+// This is the default handler for interrupts, if triggered but not defined.
+.section .text.Default_Handler
+.global  Default_Handler
+.type    Default_Handler, %function
+Default_Handler:
+    wfe
+    b    Default_Handler
+
+// Avoid the need for repeated .weak and .set instructions.
+.macro IRQ handler
+    .weak  \handler
+    .set   \handler, Default_Handler
+.endm
+
+.section .isr_vector
+.global  __isr_vector
+    // Interrupt vector as defined by Cortex-M, starting with the stack top.
+    // On reset, SP is initialized with *0x0 and PC is loaded with *0x4, loading
+    // _stack_top and Reset_Handler.
+    .long _stack_top
+    .long Reset_Handler
+    .long NMI_Handler
+    .long HardFault_Handler
+    .long MemoryManagement_Handler
+    .long BusFault_Handler
+    .long UsageFault_Handler
+    .long 0
+    .long 0
+    .long 0
+    .long 0
+    .long SVC_Handler
+    .long DebugMon_Handler
+    .long 0
+    .long PendSV_Handler
+    .long SysTick_Handler
+
+    // Define default implementations for interrupts, redirecting to
+    // Default_Handler when not implemented.
+    IRQ NMI_Handler
+    IRQ HardFault_Handler
+    IRQ MemoryManagement_Handler
+    IRQ BusFault_Handler
+    IRQ UsageFault_Handler
+    IRQ SVC_Handler
+    IRQ DebugMon_Handler
+    IRQ PendSV_Handler
+    IRQ SysTick_Handler

targets/lm3s6965.ld

@@ -0,0 +1,10 @@
+
+MEMORY
+{
+    FLASH_TEXT (rw) : ORIGIN = 0x00000000, LENGTH = 256K
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 64K
+}
+
+_stack_size = 4K;
+
+INCLUDE "targets/arm.ld"

targets/qemu.json

@@ -0,0 +1,20 @@
+{
+	"llvm-target": "armv7m-none-eabi",
+	"build-tags": ["qemu", "lm3s6965", "arm", "js", "wasm"],
+	"linker": "arm-none-eabi-gcc",
+	"compiler-rt": true,
+	"pre-link-args": [
+		"-nostdlib",
+		"-nostartfiles",
+		"-mcpu=cortex-m0",
+		"-mthumb",
+		"-T", "targets/lm3s6965.ld",
+		"-Wl,--gc-sections",
+		"-fno-exceptions", "-fno-unwind-tables",
+		"-ffunction-sections", "-fdata-sections",
+		"-Os",
+		"targets/cortex-m.s"
+	],
+	"objcopy": "arm-none-eabi-objcopy",
+	"emulator": ["qemu-system-arm", "-machine", "lm3s6965evb", "-semihosting", "-nographic", "-kernel"]
+}